1. Technical Field
This invention relates to fiber reinforced ceramic matrix composite parts in sliding relationship to one another and, more particularly, to a method of forming a structural fiber reinforced ceramic matrix composite part having improved erosion resistance of its outer surface comprising the steps of forming the part from a pre-ceramic resin having fibers of a woven or non-woven generic fiber system disbursed throughout; firing the part at a temperature and for a time which converts the resin into a ceramic; and, coating the wearing surface with an erosion-resistant material.
2. Background Art
Composite material structures are very popular for various uses. The most widely known such structure is that of so-called "fiberglass" which is used for everything from boats to bathtubs. Such structures are easy to construct employing a mold. For a fiberglass boat, for example, the inside of a female mold is first coated with a parting agent to prevent the final boat from sticking to the mold. The mold is then covered with a color coat of the resin material. The resin material is a viscous liquid to which a hardening agent is added at the time of use. Due to a chemical reaction, the resin turns hard after a short period of time without the need for any further action. Once the color coat is in place, the builder adds layers of a class fiber cloth mat material which are saturated with the liquid resin containing the hardener. The cloth mat containing the resin is rolled and pressed in place to add strength to the final structure. When the resin has hardened, the boat is removed from the mold. At that time, seats and other required parts can be added to the interior of the boat.
More recently, fiber reinforced ceramic matrix composite (FRCMC) structures have been made available for use where due to high temperatures (greater than 400.degree. F.) fiberglass is not suitable. While fiberglass will burn readily, FRCMC, being a ceramic, withstands heats that can destroy even metals. The typical prior art FRCMC structure is made in the manner depicted in FIGS. 1 and 2. A cloth mat of a generic fiber system of, for example, Alumina, Altex, Nextel 312, Nextel 440, Nextel 510, Nextel 550, Silicon Nitride, Silicon Carbide, HPZ, Graphite, Carbon, or Peat is used in place of the glass fiber cloth mat of fiberglass. A pre-ceramic polymer resin such as Silicon-Carboxyl resin sold by Allied Signal under the trade name Blackglas, Alumina Silicate resin (commercially available through Applied Poleramics under the product description CO2), or a cementatous resin modified to emulate polymer composite processing techniques such as Monoaluminum Phosphate (also known as Monoalumino Phosphate) resin is combined with the mat 10. The structure is then heated under pressure to form a dense pre-ceramic "polymer form". The as-formed pre-ceramic shape is then heated for a time to a temperature, as specified by the material suppliers (typically between 1,500.degree. F. and 2,000.degree. F.) which causes the resin 12 to convert into a ceramic material. The resultant FRCMC structure 14, therefore, comprises a ceramic resin 12' containing fibers 16 of the woven or nonwoven cloth mat. There are many methods which can be used to manufacture fiber reinforced ceramic matrix composites. The polymer-derived FRCMC fabrication method described herein is only one such method. Other methods include depositing the matrix around the fiber preform by means of chemical vapor deposition, reaction bonding, hot melting of glasses, and sintering of ceramic powders under extreme pressures and temperatures. The polymer-derived FRCMC manufacturing method is emphasized in this invention because it is the preferred method for the manufacture of the related inventions. Additionally, there are many manufacturing methods available under the Polymer Derived FRCMC fabrication umbrella. Some of these other polymer processing methods include, but are not limited to, resin transfer molding (RTM), short fiber injection, casting, hot pressing, and pultrusion, filament winding (also known as toe placement). Also, the use of a wide range of fiber forms is possible when using polymer process techniques. Fiber can be supplied in rigid or binderized preforms, woven or braided preforms, random mat preforms, fabric, toe (thread), or chopped toe or fabric. Each of the polymer composite manufacturing methods can be used with one or more of the bulk fiber forms .
In a co-pending application entitled HIGH-EFFICIENCY, LOW-POLLUTION ENGINE by the inventors herein filed on even date herewith and assigned to the common assignee of this application, an improved structural FRCMC material is disclosed having high breakage resistance and particular applicability to use for parts in a high temperature internal combustion engine.
To date, the prior art has used FRCMC materials for parts which are not intended to be in a predominately sliding, contacting relationship such as aircraft hot structural components. Attempts by the inventors herein to employ FRCMC structures for parts in a sliding, contacting relationship such as a piston in the cylinder of an automobile resulted in the eventual deterioration of the parts at their interfacing surface. The reason can be seen and understood with reference to FIG. 3. While shown exaggerated for purposes of easy understanding, the fibers 16 of the cloth mat are woven in the usual manner for cloth materials. Thus, there is a bending of the fibers 16 as the "fill" and "warp" fibers pass over and under one another. As the two FRCMC structures 14 are slid over one another in contacting relationship as depicted by the arrow 18, the tips of the fibers 16 at the surface break and chip. The material of the fibers 16 being harder than the ceramic resin 12', the broken and sharp tips of the fibers 16 dig at and eat away the surrounding ceramic resin 12'. And, the disintegration is an increasing process. As more of the fibers 16 are released from the constraints of the surrounding ceramic resin 12' as it is eaten away, there are more broken fibers 16 and longer exposed fibers 16 to dig deeper within the structure, further erode, and ultimately destroy it. Although this wear phenomenon is most prevalent in woven fabric composites, similar and less extensive wear phenomenon of this nature occur in all FRCMCs regardless of fiber architecture.
Wherefore, it is an object of this invention to provide a FRCMC structure regardless of fiber architecture and method of manufacture which will withstand sliding, contacting interaction without erosion thereof.
Other objects and benefits of this invention will become apparent from the description which follows hereinafter when read in conjunction with the drawing figures which accompany it.